a. Field of the Invention
The present invention concerns a method and apparatus for performing false-twisting of filament yarns to produce crimped filament yarns.
B. Description of the Prior Art
Conventional false-twisting apparatuses may be divided roughly into the following two types, one of which is the so-called spindle system type and the other may be termed as the friction system type.
The known false-twisting apparatuses of the spindle type may further be divided into the two sub-types, one of which is arranged so that the spindle is contact-driven by a drive roller made of rubber. In actual operation of this type of apparatus, the spindle is rotated usually at the rate of the order of 350,000 - 450,000 r.p.m. at the most. In view of the fact that the velocity of travel of the filament yarn which is being processed is determined in proportion to the rotation speed of the spindle, the productivity of the aimed crimped filament yarn, accordingly, is determined by the rotation speed of the spindle, and no further improvement in the productivity can be expected beyond this level unless the rotation speed of the spindle is increased. Moreover, those spindles which are employed in the conventional false twisters of this type are such that their twister pins are heated due to the friction produced by the drive rollers. In addition, the filament yarn which is heated to produce crimps therein is passed therethrough while being rotated axially. Therefore, the twister pin is subjected to further heating and the temperature thereof inconveniently increases higher to a level above the secondary transfer point of the original filament yarn.
The other type of the false-twisting apparatus of the prior art which employs the spindle system is represented by an apparatus comprising a turbine-blade type high speed rotary member having blades formed on its outer periphery and having a filament yarn passageway formed axially therethrough and a twister pin provided in this passageway, said rotary member being supported by fluid-bearing within a casing, said rotary member further comprising means for jetting a pressurized fluid onto the blades of said rotary member. During the operation, the twister pin is cooled indirectly by said pressurized fluid to prevent an elevation of the temperature of the twister pin. The apparatus of this type allows the productivity of crimped yarn which is almost doubled as compared with that of the first-mentioned type. However, according to such known type of false-twisting apparatus, the processing speed, as measured in terms of the running speed of the filament yarn, is 100 m/min. .about. 150 m/min. at the most. Above this level, the filament yarns which are subjected to a false-twisting process tend to develop a number of hair or fluffs and breakage of filament yarns resulting in rejectable yarns.
In the false-twisting apparatuses of these known types, it is mandatory that the pull-out tension of the filament yarn has to be greater than the tension of the filament yarn located on the twisting zone. In order to raise productivity, the spindle which is required one for each filament yarn has to be rotated at a ultra-high speed and also the pull-out tension is required to be increased. However, with an increase in the pull-out tension which is applied onto the filament yarn to be processed, there suddenly arises an increase in the number of development of hair or fluffs in the filament yarns and the number of broken yarns, so that no crimped filament yarns of the desired good quality can be obtained.
As stated previously, there have been proposed various types of false-twisting apparatuses of the so-called friction type. Apparatuses of this type of the prior art employ either at least two belts having their working surfaces arranged to frictionally engage a filament yarn successively during the run of these belts in opposite directions, said working surfaces of the belts having a large friction coefficient; or the apparatuses employ frictionally engaging rotary members such as rigid disks or conically-shaped rotary members having spiral row of ridges formed on the surfaces of these rotary members. In each of these two kinds of apparatuses, a filament yarn is fed between the surfaces of the frictional running disks or rotary members for engagement with these two surfaces of the running rigid disks or rotary members for contact therewith to be twisted thereby. While the false-twisting apparatuses relying on the surface friction system allow a higher processing rate as compared with the spindle type apparatuses, the filament yarns are, as stated above, twisted by the friction force between the filament yarns and the high friction members, and thus there is required a certain amount of tension for twisting operation. As compared with the false twisting operation of the spindle type wherein a filament yarn is turned once around the twisting pin to insure an unfailing twist, the friction system is poor in the processing efficiency such that there easily develops "stick slip" between the filament yarn and the high friction members, resulting in the development of portions of uneven twists which, in turn, tend to cause non-twisted portions remaining in the crimped filament yarns produced. Along therewith, according to the false twisting system relying on the friction system, the tension applied on to the filament yarn in the de-twisting zone, i.e. in the zone where the filament yarns are delivered from the twisting apparatus, increases with an increase in the processing rate, i.e. the running speed of the filament yarns. For this reason, the operation is accompanied by the tendency to develop breakage of the filament yarns and development of hair or fluffs in the filament yarns during the false-twisting operation, causing a reduction in the productivity and the lowering of the quality of the products. Thus, according to the apparatuses of the friction type, the maximum limit of practical processing rate is the order of 500 - 600 meters per minute. Furthermore, the number of twists or turns imparted to the filament yarn in such known type of false-twisting apparatuses is knwon either by sampling the running filament yarn and by measuring the number of the actual turns thereof or by just an inference alleging from the tension applied to the filament yarn being twisted by giving reference to the predetermined mutual relationship between the actual turns and the tension applied onto the filament yarn at the time of twisting. Thus, in the prior art, it is difficult to make accurate control of the number of turns imparted to the filament yarns being processed.
As still another type of known friction-type false twisting apparatus, there is one comprising two rotary disks each having a ridge of ring shape provided on the circumference thereof, said rotary disks being brought into contact with each other, with the centers of these two rotary disks being offset relative to each other, so that a filament yarn is fed through the site of contact of these two rotary disks for being twisted. With such known false twisting apparatus, it will be noted that, in order to have a filament yarn nipped positively between the two rotary disks, there is required a relatively great pressure of contact between the two rotary disks. This, in turn, tends the ridged portions of the rotary disks to become easily worn out, so that it is difficult to perform false twisting of a filament yarn with stability throughout the twisting operation.
In order to avoid such wear-out of the rotary disks, there has been proposed to pass a bundle of yarns between a pair of belts which are spaced from each other with a narrow distance therebetween. It has been noted however, that with such an apparatus, it is difficult to have a fine filament yarn nipped between such pair of belts. Thus, it is not possible to perform a stabilized false twisting operation.